The present invention concerns a procedure for measuring thermal energy transported with the aid of fluid flow. The procedure of the invention is appropriate for measurement both of the increase and decrease of the heat contents in the heat-transporting fluid. The commonest area of application of the procedure is a commercial area heating distribution network, specifically for each house or for each area. The fluid transporting thermal energy may be any uniformly flowing fluid as regards its state of aggregation and its chemical composition, its most important characteristic being a high specific heat value.
Present-day heat quantity or thermal energy measurement techniques are based on separate measurement of a temperature differential .DELTA.T=T.sub.1 -T.sub.2 and separate measurement of a volumetric flow V, the rate of change of thermal energy content then being: EQU Q=.rho..multidot.CV(T.sub.1 -T.sub.2)
where .rho.=density of the fluid and C=specific heat. The measurement of density of the fluid and specific heat is completely omitted nowadays, implying that no provision is made for their variations. If steps are taken to employ as thermal energy-transporting fluid, water which has been improved with additive substances, it is well conceivable that .rho.C may not always be as constant as is the case with pure water.
Of the various quantities to measured, V is substantially less accurate than .DELTA.T; if endeavours are made to improve the measuring accuracy of V, this leads to very expensive meters, such as e.g. the inductive (magnetic) flow meter, which has a metering error amounting to (.+-.0.5% of the reading)+(.+-.0.5% of full scale deflection).
The limitations imposed by area heating technology on the developing of the method of measurement--to mention a few of them--are:
the meter must not cause any significant increase in demand of pumping work; the upper limit for the pressure drop is quite generally 0.1 bar;
the power consumption of the meter should be minimized, and it must not exceed 0.1% of the thermal energy rate that is being measured;
the price at which the meter sells should be concordant with the savings regarding errors in the charging, owing to heightened accuracy of measurement.